1. Field of the Invention
The present invention relates to a method for lining a pipe by applying a lining material on the inner wall of the pipe, and in particular the invention relates to a method for lining a branch pipe branching off a main pipe.
2. Description of the Prior Art
When an underground pipe, such as pipelines and passageways, becomes defective or too old to perform properly, the pipe is repaired and rehabilitated without digging the earth to expose the pipe and disassembling the sections of the pipe. This non-digging method of repairing an underground pipe has been known and practiced commonly in the field of civil engineering. Typically, the method is disclosed by Japanese Provisional Patent Publication (Kokai) No. 60-242038.
According to this publication, this method of pipe repair comprises inserting a sufficiently long tubular flexible liner bag into the pipe to be repaired by means of a pressurized fluid, like air and water. The tubular liner bag is made of a flexible resin-absorbent material impregnated with a thermosetting resin, and has the outer surface covered with an impermeable plastic film. More particularly, according to the publication, the tubular flexible liner bag is closed at one end and open at the other; the tubular flexible liner bag is first flattened, then, the closed end of the tubular liner bag is tied to a control rope; the open end of the tubular liner bag is made to gape wide and hooked (anchored) at the end of the defective or old pipe in a manner such that the wide-opened end of the liner completely and fixedly covers and closes the pipe end; a portion of the liner is pushed into the pipe; then, the pressurized fluid is applied to the said portion of the tubular liner such that the fluid urges the tubular liner to enter the pipe. Since one end of the tubular liner is hooked at the end of the pipe, it remains there while the rest of the flexible liner bag is turned inside out as it proceeds deeper in the pipe. (Hereinafter, this manner of insertion shall be called "everting". ) When the entire length of the tubular liner bag is everted (i.e., turned inside out) into the pipe, the control rope holds the closed end of the tubular liner bag to thereby control the length of the tubular liner in the pipe. Then, the everted tubular liner is pressed against the inner wall of the pipe by the said pressurized fluid, and the tubular flexible liner is hardened as the thermosetting resin impregnated in the liner is heated, which is effected by heating the fluid filling the tubular liner bag by means of a hot steam, etc. It is thus possible to line the inside wall of the defective or old pipe with a rigid liner without digging the ground and disassembling the pipe sections.
This method is applicable to a pipe branching out from a main pipe as well, and how it is conducted will be described next with reference to FIG. 12.
FIG. 12 is a vertical sectional view of a sewerage site, showing the conventional method of lining a pipe 103 branching out from a main pipe 101. The branch pipe 103 is normally tilted, rather than vertical, in a manner such that the flow of the liquid down the branch pipe 103 acquires a momentum to rush downstream when it enters the main pipe 101. In other words, of the two supplementary angles formed between the branch pipe and the main pipe, the one on the downstream side of the main pipe is greater. Therefore, in FIG. 12, the downstream of the main pipe 101 is to the left. As shown, a flexible tubular liner bag 104 is everted in the underground branch pipe 103 from the ground by means of the pressure of the water supplied from a water hose 108. When the length of the tubular liner bag 104 is substantially greater than the length of the branch pipe 103, then the head of the tubular liner bag 104 hits upon the inner wall of the main pipe 101 and is thus prevented from everting longer. As a result, there occurs an uneverted portion 104a of the liner bag 104. That part of the liner bag 104 which entered the main pipe 101 is removed by cutting operation.